This invention relates to an improved chain, especially to a chain used on a bicycle.
Typically, a multi-sprocketed bicycle has front chain rings operatively connected with a rear free wheels by a chain, being controlled by a derailleur. Referring to FIG. 7, a modern bicycle is equipped with front chain rings 8 with up to three sprockets and a rear free wheels 9 with up to seven sprockets to possibly obtain twenty-one different gear ratios to suit different road conditions. The front chain rings 8 includes front sprockets 81, 82, and 83, arranged in a diametrical sequence with the smallest diametered front sprocket 81 closest to the bicycle 7. The rear free wheels 9 includes rear sprockets 91, 92, 93, 94, 95, 96, and 97, arranged in a diametrical sequence with the largest diametered rear sprocket 97 closest to the bicycle 7. The front sprocket 83 is connected with the rear sprocket 97 by a chain (shown in a phantom line). A radius difference "a" between two adjacent front sprockets is greater than a radius difference "b" between two adjacent rear sprockets. As a result, when a rider shifts, teeth of the rear sprockets can smoothly insert into the chain, but teeth of the front sprockets cannot quickly insert into the chain.
When a rider shifts up, referring to FIG. 8, a chain with a space "A" defined by two inner chain plates or a space "B" defined by two outer chain plates is received by a tooth 920 of a larger diametered sprocket, e.g., the sprocket 92; or shifts down, referring to FIG. 9, the chain is received on a smaller diametered sprocket, e.g., the sprocket 91, suiting different road conditions, such as flat or hilly. A conventional derailleur cooperating with a traditional chain does not allow the rider to shift quickly.
Referring to FIG. 10, it is found that while the rider is shifting, a top surface of a tooth of a sprocket abuts a lateral face of the chain plate according to prior art. As a result, the sprocket can not insert immediately into the space of the chain, thus delaying the rider since he has to continuously pedal to make the sprocket engage with the chain.
In the inventor's co-pending U.S. patent application Ser. No. 07/637,293, U.S. Pat. No. 5,066,265, referring to FIG. 11, a chain link includes two outer chain plates with inwardly inclines on tops and bottoms thereof and two inner chain plates with inwardly inclines on tops and bottoms thereof, so that the sprocket can insert easily and smoothly into the space of the chain.
Although the chain in accordance with the inventor's co-pending application can quickly engage with an intended rear sprocket when shifting, it can not quickly engage with an intended front sprocket when shifting up, as the radius difference "a" between two adjacent front sprockets is larger than the radius difference "b" between two adjacent rear sprockets.